This invention relates to the purification of non-aqueous polymer solutions and more particularly to elimination of the hazy, cloudy or milky appearance often observed in organic solutions of polymers prepared by anionic polymerization.
A common occurrence when redissolving in an organic medium polymers synthesized with an anionic initiator is a cloudy, milky or hazy appearance indicative of a residue of the polymerization reaction. Usually, the polymer solution directly resulting from the anionic polymerization will be clear and the cloudy condition will appear when the polymer is isolated and redissolved. Sometimes the hazy appearance also occurs upon aging of a polymer solution directly resulting from the synthesis. Purification is exceedingly difficult to achieve by conventional filtration practiced alone or with filtration aids. For example, the impurities have been found resistant to treatment with adsorbents such as alumina, talc, silica gel, various forms of alumina, clays and carbon black. The impurities in such solutions have also been found resistant to conventional salting out techniques using materials such as sodium chloride, sodium acetate, sodium carbonate, sodium bicarbonate and calcium carbonate.
Removal of the impurities is important for many commercial uses of the polymers and organic diluent solutions of such polymers, for example when the polymers are intended for use as clear top coats for laminates and other substrates, or in adhesives. In this specification the term "impurity" or similar term means an undesired material in an organic diluent solution of such polymers observable as a cloudy, milky or hazy condition, and "purification" means total removal or substantial reduction of such material.